During the course of the five-year study, asthma symptoms among school-aged children doubled on high traffic days. In particular, wheezing was found to worsen as children were exposed to soot particles from truck exhaust.

Between 21 and 23 percent of elementary school students in the South Bronx exhibit asthma symptoms. This section of New York City also has some of the highest number of hospital admissions for asthma.

The South Bronx is a busy traffic area with miles of expressways and interstates. The routes are used by trucks to access waste-transfer stations, sewage plants and wholesale markets. Children are constantly exposed to pollution while walking to schools that are in close proximity to the highways.

In the NYU study, groups of school-aged children from public schools in the South Bronx were given backpacks equipped with pollution monitors. All of the children had asthma and walked to their elementary schools.

The monitors were checked daily to assess the level of carbon concentrates taken from the air samples of the commuting students. Data was collected on their respiratory symptoms and lung function at the same time.

The daily average exposure to tiny pollution particles ranged from 20 to 50 micrograms per cubic meter. The Environmental Protection Agency (EPA) recommends a daily limit of no more than 35 micrograms per cubic meter. This limit was exceeded on about one-third of the study days.

Researchers believed soot from diesel exhaust contributed the most to the children's adverse health problems. Airborne particles found in soot and smoke are small enough to become lodged deep in the lungs.

Previous EPA studies have linked this type of pollution to asthma, respiratory problems, and reduced lung function. In the United States, asthma is the leading cause of chronic illnesses in children. An asthma attack can cause wheezing, coughing and shortness of breath.

Results of the study were made available in a press release from New York University. The authors note that the study will be published in a scientific journal next year.